Unsuspected Pneumothorax on Abdominal CT: Is a Chest Tube Needed?

ABSTRACT & COMMENTARY

Source: Brasel K, et al. Treatment of occult pneumothoraces from blunt trauma. J Trauma Inj Infec Crit Care 1999;46:987-991.

Adult blunt trauma victims admitted to either of two institutions were prospectively randomized to either tube thoracostomy or observation for occult pneumothorax (PTX), defined as PTX seen on abdominal CT scan but not on AP chest radiograph as interpreted by the trauma chief resident or attending. Positive pressure ventilation was not an exclusion criterion. Although 86 patients with 98 occult PTXs were eligible, only 39 patients with 44 PTXs were enrolled. This was attributed to a variety of reasons, including physician judgment, refusal to give informed consent, and delay in diagnosis; in roughly one-third of the unenrolled patients, the reason for exclusion could not be determined.

Respiratory distress and PTX progression were the main outcome measures. There was no significant difference between groups in either of these two parameters. The three patients (14%) that did develop respiratory distress in the observation group did so for reasons unrelated to their PTX. Three patients in the observation group developed progression of PTX; two were on positive pressure ventilation and received chest tubes, while the other was observed and did well. Across groups (treated, observed, and unenrolled), PTXs that progressed tended to be larger (defined, as in previous literature, as 5 ´ 80 mm), although this did not reach statistical significance. The authors conclude that these occult PTXs can be cautiously observed without tube thoracostomy, even if the patient will be on a ventilator.

Comment by Richard Harrigan, MD, FAAEM, FACEP

As the authors acknowledge in their discussion, this study is at odds with previous literature, both prospective and retrospective, regarding the need for a chest tube for occult PTX in patients that will be receiving positive pressure ventilation. As the discussants mention in the feature that follows the paper, this study has the methodologic concern of selection bias, as more than half of the eligible patients were not enrolled. Moreover, the incidence of complications, which were the main outcome measure, was small. Further study is probably needed before this study is embraced fully, particularly since, in an earlier study, eight of 15 patients on positive pressure ventilation randomized to the observation arm developed progression of their PTXs, and two developed tension PTX.1 Possible explanations offered for these discrepant findings included changes in ventilator management philosophy, with a more recent trend toward lower tidal volumes and lower peak airway pressure limits.

Reference

1. Enderson BL, et al. Tube thoracostomy for occult pneumothorax: A prospective randomized study of its use. J Trauma 1993;35:726-730.

In the study by Brasel et al on the need for chest tube with occult pneumothorax (PTX), which of the following statements is true?

a. All patients on positive pressure ventilation eventually needed a chest tube.

b. Occult PTXs secondary to penetrating trauma did better than those due to blunt trauma.

c. Occult PTX was defined as PTX not seen on the initial plain chest film or CT scan of the abdomen.

d. Observation of occult PTX was not associated with an increased risk of PTX progression or respiratory distress, but the incidence of these complications was low.